Compression check SuperAlce - values?
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Richard Harding
Jul 7, 2025, 4:08:16 AMJul 7
to Guzzi Singles
Hi,
I've put several hundred miles on my SuperAlce and I pulled the plug after a longish ride and its quite black and sooty so on face of it appears to be running rich but before I fiddle with the carb (I think my only option there is to lower the needle a notch?) I want to check the compression - what sort of values should I be looking for?
Anything else I should check? (valve clearances are good)
Cheers
Richard
RICHARD YAMANE
Jul 7, 2025, 11:57:57 AMJul 7
to guzzi-...@googlegroups.com
If you suspect a problem, a leakdown test is better. Besides showing if there is a loss of compression, it can tell you immediately where the problem is.
If the deposits on the plug are dry you probably don't have an oil control problem. Other things to look at would be to make sure the choke slide is being pulled up all the way. Check the float level. A high float level will cause rich running. The slide needle and needle jet should be inspected as closely as possible. If they are available for your carb you might want to go ahead and order them whether you need them now or not as a lot of the older Dellorto parts are get scarce. Eurocarb in the UK makes some parts but not all. Slides are prone to wear too but normally cause a lean condition.
Basic stuff would include a clean airfilter and if the bike is new to you, where it came from and if jetting requirements could be different in your locality.
If the deposits on the plug are dry you probably don't have an oil control problem. Other things to look at would be to make sure the choke slide is being pulled up all the way. Check the float level. A high float level will cause rich running. The slide needle and needle jet should be inspected as closely as possible. If they are available for your carb you might want to go ahead and order them whether you need them now or not as a lot of the older Dellorto parts are get scarce. Eurocarb in the UK makes some parts but not all. Slides are prone to wear too but normally cause a lean condition.
Basic stuff would include a clean airfilter and if the bike is new to you, where it came from and if jetting requirements could be different in your locality.
Rick Yamane
Importer of Vape/Powerdynamo ignition systems and Polisher of bikes at Motion Pro
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Richard Harding
Jul 8, 2025, 11:23:25 AMJul 8
to Guzzi Singles
Thanks Rick, I was getting just over 100psi on a compression test - I'll see if I can get hold of a leak down tester just for curiosity, I also used a cheap endoscope camera on my phone and it looks pretty dry, no obvious sign of oil getting past - plug was dry, just very sooty
It looks like I can get a slide needle and jet from euro carb but they list a few options for the part number 1160 (the carb is an MD27F) - https://www.dellorto.co.uk/shop/dellorto-motorcycle-carburettors-parts/dellorto-vintage-carburettors-and-parts/rc-rd-parts/1160-dellorto-l-type-needle-rc-rd-mc-md/
The variants listed are L3, L5 and L6 - the dellorto parts book lists mine as 1160 x 08 - no idea if that translates to L8 for example
similar with the main jet - https://www.dellorto.co.uk/shop/dellorto-motorcycle-carburettors-parts/dellorto-vintage-carburettors-and-parts/1102-main-jet/
In the meantime, I've lowered the needle in the slide and I'll see what effect that has
RICHARD YAMANE
Jul 8, 2025, 12:10:17 PMJul 8
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Oil will also leave heavier build up on the plug. Literally black blobs of burnt oil if bad enough.
You are probably just rich. Over time an excessively rich mixture will wash oil of the cylinder and lead to premature piston, ring and cylinder wear. Puffs of bluish smoke are an indication of engine condition too. A guide there is if it smokes going uphill that means rings, going downhill means valve guides.
The slide number I interpret as 1160 calling out the main slide number. The following number will usually indicate the cut away. That's the bevel cut on the backside of the bottom of the slide. A larger cut away is leaner. The number typically calls out the height of the cutaway in millimeters. Usually the factory calibration is best but...... :-)
Lowering the needle should help and if it does I'd consider a new needle and needle jet as they do wear which will create a rich condition. Maybe due to my off-road experience I like to keep the needle in the middle settings so you have someplace to go when riding in the mountains with elevation changes.
I had to change some jetting on the little Morini I'll be riding in the Giro di California this year as it was rich. I replaced the needle and jet, also the slide. The slide mainly because it felt like it was hanging up when trying to roll the throttle open, potentially dangerous at intersections. The needle jet was only available in a leaner size. The bleed holes in the side being different heights. I also ordered some other main and pilot jets in case the needle jet threw off other calibrations. Jetting is time consuming and can be frustration but can be very rewarding when finally right. Pick a nice day and enjoy the test rides.
You are probably just rich. Over time an excessively rich mixture will wash oil of the cylinder and lead to premature piston, ring and cylinder wear. Puffs of bluish smoke are an indication of engine condition too. A guide there is if it smokes going uphill that means rings, going downhill means valve guides.
The slide number I interpret as 1160 calling out the main slide number. The following number will usually indicate the cut away. That's the bevel cut on the backside of the bottom of the slide. A larger cut away is leaner. The number typically calls out the height of the cutaway in millimeters. Usually the factory calibration is best but...... :-)
Lowering the needle should help and if it does I'd consider a new needle and needle jet as they do wear which will create a rich condition. Maybe due to my off-road experience I like to keep the needle in the middle settings so you have someplace to go when riding in the mountains with elevation changes.
I had to change some jetting on the little Morini I'll be riding in the Giro di California this year as it was rich. I replaced the needle and jet, also the slide. The slide mainly because it felt like it was hanging up when trying to roll the throttle open, potentially dangerous at intersections. The needle jet was only available in a leaner size. The bleed holes in the side being different heights. I also ordered some other main and pilot jets in case the needle jet threw off other calibrations. Jetting is time consuming and can be frustration but can be very rewarding when finally right. Pick a nice day and enjoy the test rides.
Rick Yamane
Importer of Vape/Powerdynamo ignition systems and Polisher of bikes at Motion Pro
To view this discussion visit https://groups.google.com/d/msgid/guzzi-singles/16a6ea01-be91-4483-8d65-c7cb75114b5an%40googlegroups.com.
guzz...@aol.com
Jul 8, 2025, 12:10:18 PMJul 8
to guzzi-...@googlegroups.com
MG Cycle in Wisconsin has a nice selection of carb parts ,,,,,,,,
Patrick Hayes had a sooty plug issue some time ago , he'll tell you what he did to correct the problem without replacing any parts.
Tim
jerry atric
Jul 10, 2025, 6:55:12 AMJul 10
to Guzzi Singles
Remember the main jet is only in play once the throttle is nearly wide open. If it doesn't need choke to start from cold, that could point to the primary circuit. First try adjusting the mixture screw to leaner. Have you been for a run without air filter fitted? It could be clogged. Have you got the right heat range plug fitted?
Richard Harding
Jul 17, 2025, 4:12:54 AMJul 17
to Guzzi Singles
so just as a follow up I lowered the needle one position and after a couple of longish runs the plug looks just about perfect now
I'm going to leave it like that for a few more miles and try and figure out what needle and jet are fitted and see if I can find replacements
Thanks for all the advice
RICHARD YAMANE
Jul 17, 2025, 11:11:08 AMJul 17
to guzzi-...@googlegroups.com
All the parts should be stamped with their values. There are comprehensive Dellorto charts online that show the standard fittings for any specific bike.
Rick Yamane
Importer of Vape/Powerdynamo ignition systems and Polisher of bikes at Motion Pro
To view this discussion visit https://groups.google.com/d/msgid/guzzi-singles/fe60e691-751c-480a-a8d4-565f8d4208bfn%40googlegroups.com.
Andrew Nahum
Jul 17, 2025, 3:07:34 PMJul 17
to guzzi-...@googlegroups.com
Well done fixing it. I’d have tried the same adjustment. Speaking as a barbarian mechanic myself, if got a good plug colour and a good engine run you have a win - I would not change anything at all now, not even a new needle and new jet. It can’t get better!
I’d put them on the shelf for another year if I had an adjustment problem I really couldn’t fix.
On 17 Jul 2025, at 16:11, 'RICHARD YAMANE' via Guzzi Singles <guzzi-...@googlegroups.com> wrote:
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